Texas Instruments LM2599SX-12/NOPB

Overview

LM2599SX-12/NOPB from Texas Instruments is a monolithic 150-kHz nonsynchronous step-down DC-DC converter delivering up to 3 A output current with fixed 12-V output, ±4% regulation over line and load, input voltage range up to 40 V, and integrated thermal shutdown and current-limit protection. It serves as a high-efficiency buck regulator in industrial power supplies and embedded system rails.

For engineers reviewing the LM2599SX-12/NOPB datasheet, LM2599SX-12/NOPB pinout, LM2599SX-12/NOPB application, or LM2599SX-12/NOPB equivalent, key selection criteria include confirmed 12-V fixed output accuracy, TO-263-7 package thermal performance, soft-start/shutdown control timing, error flag delay behavior, and compatibility with standard off-the-shelf inductors.

Technical Context

The LM2599SX-12/NOPB implements a fixed-frequency (150 kHz) current-mode buck topology with internal compensation, enabling stable operation with minimal external components. Its internal switch features 1.4-V typical saturation voltage at 3-A load and supports discontinuous conduction mode for light-load efficiency.

Functional integration includes a dual-function Shutdown/Soft-start pin (logic-controlled shutdown with capacitor-programmable ramp), open-collector Error Flag with 5% dropout detection and programmable delay via external capacitor, and feedback sensing referenced to 1.23-V internal reference - all operating across –40°C to +125°C junction temperature.

Key Specifications

Pinout & Package

LM2599SX-12/NOPB is supplied in a 7-pin TO-263 (KTW) surface-mount package with exposed thermal pad, measuring 10.10 mm × 8.89 mm, optimized for PCB copper area heat spreading.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar step-down regulator applications.

Compared with LM2599T-12, LM2599SX-12/NOPB offers superior thermal performance in surface-mount layouts; versus LM2678-12/NOPB, it provides integrated error flag timing but requires larger passive components due to lower 150-kHz frequency.

Availability

LM2599SX-12/NOPB is available at Aetrix Electronics and suitable for industrial power supplies, embedded system rails, motor driver logic supplies, and test equipment auxiliary rails requiring stable component supply, long-term lifecycle assurance, and traceable sourcing.

Supply support for LM2599SX-12/NOPB includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and power management ICs, with decades of expertise in high-reliability power conversion solutions.

The LM2599 SIMPLE SWITCHER® product line was designed for ease-of-use in cost-sensitive, medium-power DC-DC applications where minimal external components, robust protection, and proven reliability are essential.

FAQ

What is the maximum input voltage rating for LM2599SX-12/NOPB?

The LM2599SX-12/NOPB has an absolute maximum input voltage rating of 45 V, with recommended continuous operation up to 40 V. Exceeding 40 V may trigger internal protection or reduce reliability; operation above 45 V risks permanent damage. The device maintains ±4% output regulation across its full 4.5–40 V input range, making LM2599SX-12/NOPB suitable for 24-V industrial buses with transient spikes.

Does LM2599SX-12/NOPB require an external feedback resistor network?

No, LM2599SX-12/NOPB does not require an external feedback resistor network. As a fixed 12-V output variant, its feedback reference is internally trimmed and configured - Pin 6 (Feedback) must be left unconnected per the datasheet. This eliminates resistor tolerance errors and simplifies layout, distinguishing LM2599SX-12/NOPB from the adjustable LM2599ADJ version which requires two precision resistors.

How does the Error Flag pin function on LM2599SX-12/NOPB?

The Error Flag pin (Pin 3) on LM2599SX-12/NOPB is an open-collector output that pulls low when the regulated 12-V output drops more than 5% (i.e., below 11.4 V). At startup, it remains low until VOUT reaches 95% of nominal (11.4 V) and the delay time set by the capacitor on Pin 5 elapses. This signal is commonly used as a power-good indicator or MCU reset source, and LM2599SX-12/NOPB guarantees flag saturation voltage ≤0.3 V at 3-mA sink current.

Can LM2599SX-12/NOPB operate in discontinuous conduction mode (DCM)?

Yes, LM2599SX-12/NOPB supports discontinuous conduction mode (DCM) at light loads or high input voltages. In DCM, the inductor current falls to zero each cycle, resulting in damped ringing on the Output pin - a normal, non-instability artifact. DCM reduces core losses and improves light-load efficiency, though peak switch current increases. LM2599SX-12/NOPB's current-limit threshold (3.6–6.9 A) and thermal protection remain fully active in DCM operation.

What thermal considerations apply to LM2599SX-12/NOPB in TO-263 package?

LM2599SX-12/NOPB in the TO-263-7 (KTW) package achieves a junction-to-ambient thermal resistance (RθJA) of 30°C/W with 2.5 in² of 1-oz copper on a single-sided PCB, or 20°C/W with 3 in² on the component side plus 16 in² on the opposite side. The exposed thermal pad must be soldered to a dedicated copper pour tied to Pin 4 (Ground); insufficient copper area will cause thermal shutdown at ≤2.2 A continuous load. LM2599SX-12/NOPB includes internal thermal shutdown at 150°C.